Carrier 42C Series Product Data page 14

Application data (cont)
System piping
SYSTEM 2 — REVERSE RETURN
The following diagrams show some common methods
used to pipe the 42S series units. Only the 2-pipe systems
are shown; however, the methods would be the same for
4-pipe systems.
System 1, the "direct return" system, is the most common.
It is economical to install since it supplies and returns the
water for a riser column from the same location, at the top
or the bottom of a building. This type of riser arrangement
does require more attention to individual unit water flow
balancing. The risers are normally capped at the end as
shown in the diagrams.
System 2, the "reverse return" system, is used to minimize
the requirement for individual unit balancing. This system
is usually referred to as the self-balancing system. The
arrangement of the risers allows the water flow for each
unit in a column to be equalized. In the reverse return sys-
tem both the supply and return mains are located at the
top or the bottom of a building requiring an additional
return riser to be furnished in the units.
System 3, the "common reverse return" system, typically
has the supply and return mains located remotely from
each other — such as one at the top and one at the bottom
SYSTEM 3 — COMMON REVERSE RETURN
of a building. This eliminates the need for a reverse return
riser in the units.
SYSTEM 1 — DIRECT RETURN
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